[ishlinea7260]

@dieseladdilkt , same thing happened to me in my linea saw "EBD FAILURE" on the MID but turned out that the brake fluid level was low. All they did was to top up the level and thats it.

[DerAlte]

Originally Posted by Sutripta

... why a split U surface will not produce unequal forces (resulting in a couple ???) when all wheels are being braked to their limits, ABS or no ABS. ...

Simple, sir, different points of reference! You are perhaps only looking at it from the road up, I have been talking ABS down. No brainer: OF COURSE mu variation will produce unequal braking IF ABS is NOT there, tending to spin the car around. That is the problem that ABS solves by doing exactly the opposite - doesn't allow wheel to lock long enough for the 'resultant' of the unequal forces to cause a significant deflection of the car.

Originally Posted by DieselAddikt

... We wanted to see how it behaves on high speed braking. So in a open road, we did a quick 130 and braked a little hard. The ABS kicked in. I could feel it. ...

WHY? What was on test - the ABS or the person? The pedal would have shuddered for 10 secs or more! <Sigh> To each his own!

Originally Posted by DieselAddikt

... The MID showed "EBD Failed - Please read Handbook" ...

1. Did either of you read the handbook ultimately? What does it say?
2. If it is only EBD that is being reported as having failed, it is most likely a benign software exception that prevented the EBD from influencing braking behavior. Could very well be low brake fluid level as @ishlinea7260 mentioned. The exact reason would be in the Error Code stored in the ABS/EBD ECU. Take the car to the A.S.S. and ask them to connect to the ECU and read the Error Code - will indicate what caused the exception and the error message. Just make sure that after whatever they do they MUST PROVE TO YOU that ABS/EBD is not malfunctioning again.

[Thad E Ginathom]

Originally Posted by ownerofazkaban

I was always under the impression that ABS 'always' increases braking distance. Am really surprised by the fact that in normal consition ABS helps reduce stopping distance ?? All manuals talk about sightly increased stopping distance esp, in gravel/loose soil the "locked wheels ploughing thru" is considered better for braking distance.

The logic goes like this:

The most efficient point of braking is just before the wheels lock; After lockup, efficiency is lost.

ABS is able to maintain the braking at that point, by not allowing the brakes to lock.

Therefore braking with ABS is more efficient, and stopping distances might be reduced, but will not be increased.

Ultimately, braking depends on the contact of your tires with the ground. If something like loose grit, water, oil or ice is getting in the way of that, all bets on stopping are off anyway!

[DieselAddikt]

@ownerofazkaban. Does that mean that the normal brakes are functioning correctly ? Or will it be a case of low brake fluid like ishlinea7260 said ?

@DerAlt. The ABS was on test.

We read the manual. It simply said something like "Go to the nearest TASC and drive cautiously."
Wanted to know if the normal braking will work efficiently now. Might be able to take the car to TASC only on weekends.

[DerAlte]

Originally Posted by DieselAddikt

... Does that mean that the normal brakes are functioning correctly ? Or will it be a case of low brake fluid like ishlinea7260 said ? ...

Brakes will function normally with low brake fluid and EBD failing - just be more cautious than usual. Anticipate braking instead of reacting at the last moment.

Originally Posted by DieselAddikt

@DerAlt. The ABS was on test.

ABS testing involves controlled conditions. Your ABS testing method can lead to a catastrophe if you encounter just a small stone. DON'T.

Originally Posted by DieselAddikt

We read the manual. It simply said something like "Go to the nearest TASC and drive cautiously."
Wanted to know if the normal braking will work efficiently now. Might be able to take the car to TASC only on weekends.

Very sensible instruction!!! Don't worry about normal braking. Don't wait indefinitely to go to the A.S.S., but do it as early as you can.

[DieselAddikt]

Good to know that the normal braking will work just fine. Will be careful though. Thank you all for the responses.

@DerAlt. The road we did this was recently paved and is a 6 laned one with proper markings. And at that point of time, the road was literally empty. We made that sure before trying this out. But yes, at 130kmph, anything can happen. Will not be attempting this again anyway.

[Sutripta]

... why a split U surface will not produce unequal forces (resulting in a couple ???) when all wheels are being braked to their limits, ABS or no ABS. ...

Yaw, spin.

Originally Posted by DerAlte

Simple, sir, different points of reference! You are perhaps only looking at it from the road up, I have been talking ABS down.

Doesn't matter which end you start tackling the problem. If solvable, result should be the same.

No brainer: OF COURSE mu variation will produce unequal braking IF ABS is NOT there, tending to spin the car around. That is the problem that ABS solves by doing exactly the opposite - doesn't allow wheel to lock long enough for the 'resultant' of the unequal forces to cause a significant deflection of the car.

As I keep on asking, how does ABS (the thing that prevents wheels from locking under extreme braking) keep the car going in a straight line when braked hard on a split U surface.

When ABS is operational, the force on each wheel (assuming independent channels for each wheel) is very close to that which is available at the knee point (threshold braking). Which will differ for different surfaces. Which should lead to different retarding forces for each side of the car (split U surface). Causing the car to spin.

Regards
Sutripta

[DerAlte]

Originally Posted by Sutripta

... Doesn't matter which end you start tackling the problem. If solvable, result should be the same. ...

No, it won't be the same. You would be missing other significant dimensions, like time.

Originally Posted by Sutripta

... When ABS is operational, the force on each wheel ... Causing the car to spin.

What one sees in a still photograph (static view) is quite different from what one sees happening in slo-mo (time sliced view). What one would be missing in the static view here is that one is never allowing other forces enough time to cause a deflection, simply by allowing the wheel to roll.

The 'threshold braking' is in direction of motion - straight line. The other odd happenings - rubber shredding, vapor lock and other such gooey stuff - which are perpendicular to the direction of motion are not able act long enough because at the next time slice the blessed wheel rolled over them. At the subsequent time slice the along-the-direction-of-travel still acted, then wheel rolled, then ... so on and so forth. The wheel on lower mu rolls longer and brakes shorter (by design, not by physics), and the one on the higher mu the reverse.

There is never any 'big bang' braking and 'big bang' yaw all at the same point of time (static view). So, even if there is different mu on 2 sides, all the wheels and the car keep going in the same direction. Under these conditions, if one moves the steering, the car docilely moves the way it is supposed to move.

This, sir, is unlike the effect that one feels with an airport trolley in which one of the bearings is kaput and drags the trolley to one side since that differential force is constantly active.

[Sutripta]

Originally Posted by DerAlte

No, it won't be the same. You would be missing other significant dimensions, like time.

As I said, if solvable.

What one sees in a still photograph (static view) is quite different from what one sees happening in slo-mo (time sliced view). What one would be missing in the static view here is that one is never allowing other forces enough time to cause a deflection, simply by allowing the wheel to roll.

The 'threshold braking' is in direction of motion - straight line. The other odd happenings - rubber shredding, vapor lock and other such gooey stuff - which are perpendicular to the direction of motion are not able act long enough because at the next time slice the blessed wheel rolled over them. At the subsequent time slice the along-the-direction-of-travel still acted, then wheel rolled, then ... so on and so forth. The wheel on lower mu rolls longer and brakes shorter (by design, not by physics), and the one on the higher mu the reverse.

There is never any 'big bang' braking and 'big bang' yaw all at the same point of time (static view). So, even if there is different mu on 2 sides, all the wheels and the car keep going in the same direction.

^^^ Mostly pointyhaired 'explanation'/ gobbledygook.

Under these conditions, if one moves the steering, the car docilely moves the way it is supposed to move.

FINALLY.

If you brake hard on a split U surface, the longitudinal (braking) forces will be different on each side of the car. This will cause the car to turn. Unless prevented by some other force. The other force is corrective steering action. Which works because ABS maintains steerability by not locking the wheels.

This is no different from using steering corrections to keep the car going straight when one has a binding brake (on one wheel), or an underinflated tyre.

Regards
Sutripta

[DerAlte]

Originally Posted by Sutripta

... Mostly pointyhaired 'explanation' / gobbledygook. ...

Originally Posted by Sutripta

... FINALLY. ... longitudinal (braking) forces will be different on each side of the car. This will cause the car to turn. Unless prevented by some other force. The other force is corrective steering action. ...

*Sadly shaking head* Problems don't get solved by expecting that all explanations must fit the mental model one is expecting, even if it is the wrong model used for analysis. Everything anyone says *will* be gobbledygook then.

I wasn't referring to corrective steering action, dada, but you seem to have stopped at differential mu, which the ABS is not allowing to act. What happens when - whatever be the mu - for x ms mu is relevant for braking and for the next x ms the same mu is relevant for the tyre to roll (since the tyre is alternately braking and rolling by ABS action)?

You are better than me at FEM, just that you are not using that technique right now. Moment mal - were you discussing differential mu effect without ABS? Your expectancy will be satisfied correctly if there is no ABS.

[Sutripta]

Originally Posted by DerAlte

*Sadly shaking head*

Me too. Me too. + add wry smile!

Problems don't get solved by expecting that all explanations must fit the mental model one is expecting, even if it is the wrong model used for analysis. Everything anyone says *will* be gobbledygook then.

Your model please.

I wasn't referring to corrective steering action, dada, but you seem to have stopped at differential mu, which the ABS is not allowing to act. What happens when - whatever be the mu - for x ms mu is relevant for braking and for the next x ms the same mu is relevant for the tyre to roll (since the tyre is alternately braking and rolling by ABS action)?

You are better than me at FEM, just that you are not using that technique right now. Moment mal - were you discussing differential mu effect without ABS? Your expectancy will be satisfied correctly if there is no ABS.

In your view, what will be the retarding forces on each wheel on a split U surface, with ABS operating on all wheels?

OT:- Posted yesterday night, edited today morning. Second thoughts somewhere??

Regards
Sutripta

[vina]

Originally Posted by Sutripta

Me too. Me too. + add wry smile!




Your model please.

In your view, what will be the retarding forces on each wheel on a split U surface, with ABS operating on all wheels?

OT:- Posted yesterday night, edited today morning. Second thoughts somewhere??

Regards
Sutripta

Allow me to gatecrash into your discussion and ask a few questions:

I guess what Sutripta sir is saying is - differential mu => different forces => torque around the CG of the vehicle causing yaw => vehicle must turn unless there is a restoring torque.

I couldn't understand Der Alt sirs reasoning (I guess he'll explain later again), but here is me thinking out loud:

Let us assume a scenario where a driver (for some reason) was driving such that left side wheels were on a slippery surface while right side wheels were on dry road (can happen e.g. with water on the road, or oil spill or whatever) and the driver slams the breaks and ABS comes into action. Let us further assume that only the front wheels matter (they matter more anyway, so this simplification should not hurt much):

With equal force applied on both left and right side wheels, the left side wheels will lock first (slippery surface) - ABS will detect this and pulse the break fluids.

• I'm assuming that only the left wheel will be pulsed, is that correct?

Assuming very good ABS system, both left and right wheel will be breaking with a force that will keep each wheel at the threshold of sliding friction (i.e. prevent the sliding) - and keep each wheel rolling.

• So the break force each wheel will exert will be slightly less than max sliding friction possible on each side - is that correct?

Assuming driver didn't steer the car, the forces in question above would be anti-parallel (i.e. opposite) to the direction of the tyres' rolling directions.

• How are the perpendicular forces expected to behave?
  • First of all, is the coefficient of friction in the forward direction same as that for the friction in the sideways direction as far as tires are concerned?
  • And if it is not, then isn't it possible that the yaw motion is prevented by extra friction seen by the tyres perpendicular to the direction of motion?

[nrajeshkumar]

Hi Guys,
Thought my father's swift vxi ABS 2006 model was just ran 25000 km. It recently started warning ABS on the dashboard and the Maruti service technician confirmed me that ABS diaphragm(I really don't know what that mean) is broken and that require a complete replacement of ABS which would cost me around 35,000. I could also feel that when I drive the brake pedal is go soft all the way down which never happened before and the break oil level drops very frequently. I took it to a different Maruti service center and they also declared the same. If anyone know if the ABS can be repaired by spending few thousands instead of replacing the whole unit kindly advice me. I want get this fixed asap, I don't want to take any risk on brakes.

Thanks,
Rajesh

[Thad E Ginathom]

You are taking a risk every inch that you drive it with faulty brakes!

You have checked out two Maruti service centres that have both told you the same thing. I think you have one option left, which is to try a trusted independent, as the car is now five years old and out of warranty.

So far, I've only been there for advice (freely given) but I intend to get my next service at Ignite (ECR). If you search for Ignite Garage here, you should find some recommendations. You might even get a straight answer on the telephone: he's a nice guy.

Good luck!

[DerAlte]

Which ABS do you have in your car - Bosch or Denso? Never heard of an "ABS Diaphragm" - perhaps you can ask them to point out which component, take a pic of that and post it here? All the components of the ABS system, including the ECU, are individually replaceable. But, the Service Center perhaps does not want to go into that headache considering lack of skills, so they will all recommend complete system replacement. The ABS ECU always records what fault is occurring / has occurred, and using a service tool the same can be read from the ECU.